FR2529511A1 - OFFSET PLATES BASED STEEL AND CHROME MULTILAYER - Google Patents

Abstract

1. Offset plates based on steel and having an aquaphilic layer of chromium comprising : - in contact with the steel, a protecting layer (A) of shiny chromium of thickness less than 0.4 mu m ; - above said protecting layer, a layer (B) of chromium with dull finish surface ; said plates being characterized in that said layer (B) is selected from : a) the layers of chromium comprising at least 400 micro-fissures per centimeter (known as micro-fissured layers) or comprising at least 40 cracks per centimeter (known as microcracked layers) ; b) the chromium layers obtained by successively depositing more than two layers of chromium, each of said layers having a thickness less than 0.5 mu m. c) or a superposition of layers a) and b) ; layer (B) having a thickness more than 1 mu m.

Description

Offset plates based on steel and multilayer chrome.

  The present invention relates to offset plates to

  base of steel (or black iron) and with multiple layers of chromium.

  Offset plates having a support of steel (or black iron), an aquaphile layer (and encrophobe) of chromium and an inkjet printer layer of photosensitive material have already been described and marketed for such plates, the layer

  chromium aquaphile must have very specific properties.

  especially in view of the fact that the surface of

  allow the attachment of the photosensitive material.

  For many years, this layer of chromium has been used as the only aquaphile layer for fixing the photosensitive material. It has therefore been necessary to use an intermediate metal which protects the surface of the support (steel or black iron) against rust This protective metal layer consisted of a soft metal generally ink-like such as copper

  or tin or nickel; the consequence of the presence

  Considered necessary of this protective metal layer in an encrophile metal covering was the systematic use of thick chromium layers (from 1 to 3 microns for example) whose surface was made matt (to allow the attachment) by

known techniques.

  Recently, new offset plates having the same general structure have been proposed by implementing two new ideas that can be expressed in the following way: it is possible to limit the thickness of the chromium layers (aquaphile, encrophobic and hooking) provided that such layers are deposited on hard and aquaphile metal layers; it is thus possible to make plates in which the chromium surface layer has a thickness of less than 1 micron and preferably less than 0.5 micron; it is possible to use chromium-based layers (so

  hard and aquaphile) for the protection of the surface of

  steel or black iron ports; in the search for the protection of said surface with the aid of thin industrial layers, a protective layer consisting of chrome chromium oxide has been described. In both cases, the printer part was provided by a resin

  photosensitive encrophil (or photopolymer).

  If the offset plates obtained by implementing these two ideas have remarkable technical properties, it appeared that, for certain applications in particular, one could have

  interest in reinforcing the protection of the surface of the

  port and on the other hand the mechanical resistance (for example to the abra-

  sion) of the chromium layer whose surface is aquaphile,

phobe and allows hanging.

  It has been found and this is the purpose of the present invention.

  It is possible to produce offset plates with a steel or black iron support and having improved properties by using as a protective layer a layer of shiny or semi-gloss chrome of slight thickness.

  as an aquaphile layer a chromium layer of greater thickness

  less than 1 micron, preferably of thickness between 1 and 2 microns, provided that this chromium layer is either a microcracked or microcracked chromium layer or a chromium layer obtained by the successive deposition of at least two microns. chromium layers each having a maximum thickness of 0.5 micron, or a superposition of these two layers; in all cases

  the surface of the chrome must be matte.

  The protective layer is a layer of bright chrome

  These layers are well known and are used for decorating and for the protection against corrosion of rust-susceptible metal surfaces in applications of the luminaire type, chromed chairs, known techniques and described for the realization of such

  layers are obviously usable in the present invention.

  tion; These techniques imply in particular that the industrial conditions

  such layers are such that the layers adhere perfectly to the support and cover it at

  In particular, electroplating with the use of

  baths working at relatively high temperatures

  (at the corners about 40 C) and if possible with a very conductive

  (addition of active fluorine) as Si F 6.

  On this protective layer, an aquaphile chromium layer with a thickness greater than 1 micron will be deposited. For such a chromium layer to have the properties

  desirable (both as regards the properties of the surface-

  of this layer, properties that have been described previously,

  as regards the mechanical properties of the layer, in particular

  to prevent the formation of cracks or breaks during handling and bending of the plate) it has been found

that it was appropriate: -

  or use a microcracked or microcracked chromium layer made one or more times or use a layered layer of chromium

elementary thin.

  The term "microcracked chromium" layer refers to a layer of chromium having at least 400 microcracks per centimeter and a layer of chromium having a chromium layer having

  minus 40 cracks per centimeter.

  The definition and production of chromium layers of this type are described in French Patent 2 e 152 627 and

2,142,014.

  According to the present invention, it has thus been found that microcracked or microcracked chromium can be used as the aquaphile layer of offset plates, in part because of its texture and also because of its surface properties since said surface can be made "matt" The second technique for producing thick layers of chromium consists in producing said layers by superposing thin elementary layers of chromium. By elementary layer, a mineleconium layer means a layer of chromium with a thickness of less than about 0. 5 micron This deposit of several successive elementary layers can be carried out in a single chromium bath (by cutting the current several times) or in several sucessive baths; of course, the last layer of

252,511

  chromium will be achieved under known conditions leading to-obtaining a layer of matte appearance for hanging

photosensitive layers.

  This surface chromium layer having a matte appearance is very important in the context of this invention; however, it has been found that the surface properties of this layer can be further improved by using at least one of the following two methods: deposition on the surface of a bright chrome flash

  deposit on the surface of a corrosion inhibitor.

  We call deposit "flash" the deposit of a layer very

  thin, generally less than 0.4 micron and preferably less than

  0.2 micron Shiny chrome is a chromium which, if deposited directly on the smooth surface of steel, would be shiny or semi-glossy (that is, crystal structure of a bright chrome) It is however obvious that the flash thus deposited will not profoundly modify the matte appearance of the surface of the chrome but this flash will have the function of closing at least partially the cracks or holes that

  appear on the surface of matte chrome.

  Corrosion inhibitors (steel and black iron) are known inhibitors used in the context of the

  The present invention is preferably of anionic type products.

  Throughout this application, the term "chrome" is understood to encompass not only chromium itself but also

  chromium-based alloys that are harder than chromium (spe-

  Cr-Mo alloys) and have the same properties

aquaphiles and encrophobes.

  The following non-limiting examples illustrate the

vention.

Example 1

  A) Realization of the first protective layer (thin glossy chrome) The protection (front and back) of three steel supports (0.3 mm thick USINOR steel plate) was carried out according to

  conventional electrolytic techniques.

  After degreasing, rinsing, pickling and rinsing the steel plate, the electrolytic chromium plating was carried out by one of the following methods: 1 plate A The plate is immersed in a bath containing 250 g / l Cr 203 and 2 5 g / l of 504 H 2; the temperature of the

  bath is 450 C and the density of 30 A / dm.

  2 plate B The plate is immersed in a bath giving rise to a microcracked chromium deposit (bath marketed under the reference 2300 WALBERG), the bath being at a temperature of 55 ° C. and using a density

current of 30 A / dm 2.

  Plate C The plate is immersed in a bath containing Cr 203 247 g / l, 504 H 2 1; 1 g / l, Si F 6 2.1 g / l (a bath of this type is described in US Patent 3,498,892); the temperature is 65 C, the current density

used is 60 A / dm 2.

  In all three tests, the electrolysis was continued for a time sufficient to obtain a chromium deposit having a thickness of about 0.4 micron. The deposit is glossy and very "covering" that is to say that penetrates well into all pores

of support.

  B) Realization of the surface layer by microcracked chromium. The plate B is used which is treated again with an identical bath (2300 Walberg) but a temperature is used.

  38 C and a current density of 35 A / dm 2.

  Thus, the deposition of a new layer (1.1

  cron) microcracked chrome having a matte appearance and a surface

  hanging well the photosensitive layers printers? micropower

  site de dep 6 t further improving the attachment of the printer layer.

  We could make the same layer of micro chrome

  cracked to the matte appearance using plates A or C.

Example 2

  Realization of a chromium layer by deposition of thin elementary layers. One of the plates A is used as starting material

or C of Example 1.

  With the aid of an electroplating bath identical to that used to obtain the plate A of the example, the deposition of three successive layers of chromium having a thickness of 0.4 microns each is carried out in a bath at 35 ° C. and with a density current in A / dm bath is in a 30 C bath with a current density of 30 A / dm 2 t In both cases, a plate is obtained which has, above the surface of the steel, four layers of chrome, the first 0.4 micron thick and the other three thick

0.4 micron each.

Example 3

  Plates A and C of Example 1 are used but in

  which the bright chromium layer was reduced to 0.11 micron.

  On these two sheets of chromium plies of matt appearance and thickness O, 45 micron each are deposited by performing electrolysis under 35 A / dn 1 and 300 C. Then, on one of the two plates> is deposited a new layer of chromium under the same conditions as those used when the first layer of shiny chrome was deposited. The plate having received this surface layer of "brilliant chrome"

  has a dull appearance but has been particularly resistant

aunt to corrosion.

Example 4

  A type B plate is used (see Example 1) covered

two layers of matte chrome.

  This plate is immersed for 20 seconds in a 70 C bath containing 19 g of monosodium phosphate and 19 g of

25295 '1

3. Sodium dichromate.

  The plate was covered with a very slight deposit of these salts; she can resist for more than 8 hours at the

corrosion by water.

  It has been shown that the plates according to the invention can without baking undergo firing (10 minutes at 220 C for example) intended to harden the immolated parts of the layer

  superficial photosensitive deposited on the surface of chromium.

Claims (3)

  1) Steel-based offset plates with a matt chrome-plated aquaphile layer, characterized in that they comprise, in contact with the steel, a thin glossy chromium protective layer over said protective layer. of chromium matte chosen from: the chromium microfissurd or microcracked layers the chromium layers obtained by the successive deposition of   minus two layers of chromium less than 0.5   cron each, or a superposition of these protective layers the surface   chromium being in all cases matte appearance.   2) Plates according to claim 1 characterized in that they have also received on the surface of the matte chrome a flash of brilliant chrome.   3) Plates according to one of claims 1 and 2   characterized in that they have also received, on the surface of the   matte chrome, a corrosion inhibitor.